scholarly journals On the Rates of Growth of Grains and Crystals in South Polar Firn

1969 ◽  
Vol 8 (53) ◽  
pp. 241-252 ◽  
Author(s):  
Anthony J. Gow
Keyword(s):  
Crystal Growth ◽  
Cross Sections ◽  
Mean Annual Temperature ◽  
Growth Data ◽  
Cross Sectional ◽  
Thin Sections ◽  
The Mean ◽  
Image Position ◽  
Rates Of Growth ◽  
Strong Linear Relationship

The size of firn crystals as a function of age has been investigated in thin sections to a depth of 49 m at the South Pole. Grain cross-sections increased in size from 0.24 mm2at 0.1 m depth to 0.63 mm2at 10 m. Crystals, as distinct from grains, increased in size from 0.18 to 0.43 mm2over the same interval, implying that grains are generally composed of just one or two crystals rather than several as is frequently contended. The mean crystal cross-section increased linearly with the age of the firn at a rate of 0.0006 mm2year−1; in 388 year old firn at 49 m the crystal size measured 0.63 mm2. Analysis of crystal-growth data from other locations in Antarctica and Greenland also revealed a strong linear relationship between the mean cross-sectional arcas (D2) of crystals (in mm2) and their ages in years (t), i.e.. The fact that the temperature dependence of the crystal growth rateKcan be expressed very satisfactorily in an equation of the formK=K0exp (E/RT) confirms predictions that crystal growth in firn is essentially analogous to grain growth in metallic and ceramic sinters. An extrapolation of available data indicates that crystal growth rates in dry firn could be expected to vary by two orders of magnitude (0.0003 to 0.03 mm2year−1) over the temperature range −60° to −15°C. A method of utilizing crystal growth-mean annual temperature data to determine accumulation rates in snow is demonstrated.

scholarly journals On the Rates of Growth of Grains and Crystals in South Polar Firn

1969 ◽  
Vol 8 (53) ◽  
pp. 241-252 ◽  
Author(s):  
Anthony J. Gow
Keyword(s):  
Crystal Growth ◽  
Cross Sections ◽  
Mean Annual Temperature ◽  
Growth Data ◽  
Cross Sectional ◽  
Thin Sections ◽  
The Mean ◽  
Image Position ◽  
Rates Of Growth ◽  
Strong Linear Relationship

The size of firn crystals as a function of age has been investigated in thin sections to a depth of 49 m at the South Pole. Grain cross-sections increased in size from 0.24 mm2 at 0.1 m depth to 0.63 mm2 at 10 m. Crystals, as distinct from grains, increased in size from 0.18 to 0.43 mm2 over the same interval, implying that grains are generally composed of just one or two crystals rather than several as is frequently contended. The mean crystal cross-section increased linearly with the age of the firn at a rate of 0.0006 mm2 year−1; in 388 year old firn at 49 m the crystal size measured 0.63 mm2. Analysis of crystal-growth data from other locations in Antarctica and Greenland also revealed a strong linear relationship between the mean cross-sectional arcas (D2) of crystals (in mm2) and their ages in years (t), i.e. . The fact that the temperature dependence of the crystal growth rate K can be expressed very satisfactorily in an equation of the form K = K0 exp (E/RT) confirms predictions that crystal growth in firn is essentially analogous to grain growth in metallic and ceramic sinters. An extrapolation of available data indicates that crystal growth rates in dry firn could be expected to vary by two orders of magnitude (0.0003 to 0.03 mm2 year−1) over the temperature range −60° to −15°C. A method of utilizing crystal growth-mean annual temperature data to determine accumulation rates in snow is demonstrated.

“Pipe-organ structures” in the Lee Formation (Pennsylvanian) of the central Appalachian Basin: animal or plant?

1992 ◽  
Vol 66 (1) ◽  
pp. 148-156 ◽  
Author(s):  
Donald R. Chesnut ◽  
James C. Cobb ◽  
Stephen F. Greb
Keyword(s):  
Cross Sections ◽  
Carbonaceous Material ◽  
Animal Origin ◽  
Pipe Organ ◽  
Cross Sectional ◽  
Thin Sections ◽  
Common Structure ◽  
Channel Form ◽  
The Individual ◽  
Vertical Tubes

A sequence of unusual vertical tubes, arranged in multiple groups, and each tube several meters high occurs in the Middlesboro Member of the Lee Formation (Lower Pennsylvanian). These structures are controversial with various interpretations suggesting either plant or animal origin. Observations supporting a plant origin include: 1) numerous C- and D-shaped, and multichambered tube cross sections are similar to fern and seed fern structures, 2) numerous membrane relicts loosely enclosing the tubes are similar to fern and seed fern tissues, 3) microscopic bundles are observed in cross-sectional thin sections, 4) presence of carbonaceous material and reported fecal pellets over a vertical distance in excess of 5 m are consistent with deteriorating plant material, not escape structures, 5) tubes are composed of casts and molds, but lack spreite or other features typical of escape structures, 6) tubes occur in clusters about one meter in diameter and are associated with coaly material at their base, which suggests that the clusters represent trees, 7) other trace fossils are absent in the enclosing sandstone, 8) tubes branch upward, which is a common structure in plants but unlikely in escape structures, 9) a coalified root structure was found at the base of the sandstone, and 10) all the tubes extend from the bottom of the sandstone to the top. The probability of burrowing animals escaping through as much as 8 m of sand with 100 percent survivorship is low.The structures may represent a stand of pteridosperms with each “tree” approximately 1–1.5 m in diameter. The individual pipe-organ structures represent aerial stems, shoots, and adventitious roots; each cluster of pipe-organ structures represents a single tree.Based upon sedimentologic features such as presence of 1) channel form, 2) scoured base, and 3) fining-upward sequence, we interpret the sandstone containing the pipe-organ structures to have been deposited in a sandy fluvial or tidal channel. The unidirectional cross-bed dips, poor sorting, occurrence only of very restrictive fauna and terrestrial flora, position of the sandstone above a possible floodplain facies, and lack of characteristic tidal structures suggest that the sandstone is more probably a sandy fluvial channel that may have minor tidal influence.

Wear Mechanism of Ceramics and Surface Topography

1986 ◽  
Vol 108 (1) ◽  
pp. 9-15 ◽  
Author(s):  
T. Hisakado
Keyword(s):  
Cross Sections ◽  
Friction And Wear ◽  
Cross Sectional ◽  
Wear Rates ◽  
Contact Points ◽  
The Coefficient Of Friction ◽  
The Mean ◽  
New Criterion ◽  
Theoretical Results ◽  
Wear Tests

Assuming that harder asperities sliding on a flat surface were semicylindrical with the hemispherical ends, whose surface consisted of a series of spherical micro-asperities, effects of the number of contact points n, total area Sp of the cross-sections of grooves ploughed by harder asperities and depth of plastic zone on the coefficient of friction and wear for ceramics were theoretically analyzed. To verify theory, wear tests with various ceramic pins and a Si3N4 disk were carried out at a sliding speed of 1.63 m/s and under load of 0.98 N with no lubrication. The sizes of wear scratches on the worn surfaces were measured by means of a Talysurf and SEM photographs. The wear rates of the pins and Si3N4 disks increased with an increase in the mean cross-sectional area Sp/n of the scratches. This trend agreed with the theoretical results, which also showed that the Sp values were proportional to the wear rates. Theory also indicated the existence of a new criterion applicable to estimation of the wear rate.

scholarly journals Biomechanical Evaluation on the Bilateral Asymmetry of Complete Humeral Diaphysis in Chinese Archaeological Populations

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1843
Author(s):  
Yuhao Zhao ◽  
Mi Zhou ◽  
Haijun Li ◽  
Jianing He ◽  
Pianpian Wei ◽  
...  
Keyword(s):  
Cross Sections ◽  
Torsional Rigidity ◽  
Distribution Patterns ◽  
Group Differences ◽  
Micro Ct ◽  
Cross Sectional ◽  
Bilateral Asymmetry ◽  
Biomechanical Evaluation ◽  
The Mean ◽  
Humeral Diaphysis

Diaphyseal cross-sectional geometry (CSG) is an effective indicator of humeral bilateral asymmetry. However, previous studies primarily focused on CSG properties from limited locations to represent the overall bilateral biomechanical performance of humeral diaphysis. In this study, the complete humeral diaphyses of 40 pairs of humeri from three Chinese archaeological populations were scanned using high-resolution micro-CT, and their biomechanical asymmetries were quantified by morphometric mapping. Patterns of humeral asymmetry were compared between sub-groups defined by sex and population, and the representativeness of torsional rigidity asymmetry at the 35% and 50% cross-sections (J35 and J50 asymmetry) was testified. Inter-group differences were observed on the mean morphometric maps, but were not statistically significant. Analogous distribution patterns of highly asymmetrical regions, which correspond to major muscle attachments, were observed across nearly all the sexes and populations. The diaphyseal regions with high variability of bilateral asymmetry tended to present a low asymmetrical level. The J35 and J50 asymmetry were related to the overall humeral asymmetry, but the correlation was moderate and they could not reflect localized asymmetrical features across the diaphysis. This study suggests that the overall asymmetry pattern of humeral diaphysis is more complicated than previously revealed by individual sections.

scholarly journals Automatic reconstruction of polycrystalline ice microstructure from image analysis: application to the EPICA ice core at Dome Concordia, Antarctica

1999 ◽  
Vol 45 (151) ◽  
pp. 547-554 ◽  
Author(s):  
Michel Gay ◽  
Jerome Weiss
Keyword(s):  
Preliminary Analysis ◽  
Structural Parameters ◽  
Ice Core ◽  
Grain Morphology ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Thin Sections ◽  
Polycrystalline Ice ◽  
Analysis Application ◽  
The Mean

AbstractA digital image-processing approach is proposed which allows the extraction of two-dimensional polycrystalline ice microstructure (grain boundaries) from thin sections observed between cross-polarisers. It is based on image segmentation of colour images. The method is applied to the preliminary analysis of the shallow ( Holocene) ice of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. Structural parameters, such as the mean cross-sectional area, shape anisotropy and grain morphology, are obtained. The interest and limitations of this automatic procedure are discussed.

A Theoretical Derivation of the Similarity of Dynamic Compaction Processes of Powder Media in Dies

1986 ◽  
Vol 108 (2) ◽  
pp. 147-152
Author(s):  
Yukio Sano
Keyword(s):  
Cross Sections ◽  
Dynamic Compaction ◽  
Simple Type ◽  
Theoretical Derivation ◽  
Cross Sectional ◽  
Density Distributions ◽  
Powder Medium ◽  
Compaction Energy ◽  
The Mean ◽  
Compaction Processes

Multiple shock compactions of powder media within a die with a rigid punch are theoretically investigated. First, similarity of dynamic compaction processes for a powder medium of a simple type is exhibited through nondimensionalized one-dimensional equations. The similarity is established after determination of three parameters, i.e., the ratio S* of the lateral surface to the cross-sectional area of the medium, the ratio M* of the mass of the punch to that of the powder medium filled in the die, and the compaction energy per unit powder volume e. The similarity indicates that the particle velocity, specific volume and pressure have the same variation with respect to nondimensional time at all points in the medium with various cross-sections and initial lengths so long as S* is kept fixed at a certain value, i.e., at the same proportional nondimensional point in the medium. The density distributions of the green compacts are necessarily identical, and so is the mean density in all compactions. Second, it is shown in one of the nondimensionalized equations that wall frictional influence in a compaction where S* → 0 is not present, while the wall frictional influence is extremely large when S* is very large, which implies that the mean densities of the compacts are larger in compactions with smaller S*. Two types of compactions can be obtained for any powder medium because the equation used is applicable to any medium.

Transport theory in anisotropic media

1978 ◽  
Vol 84 (3) ◽  
pp. 549-567 ◽  
Author(s):  
M. M. R. Williams
Keyword(s):  
Cross Sections ◽  
Transport Theory ◽  
Boltzmann Transport Equation ◽  
Anisotropic Media ◽  
Particle Scattering ◽  
Boltzmann Transport ◽  
Cross Sectional ◽  
Cross Sectional Dependence ◽  
Fixed Axis ◽  
The Mean

AbstractWe develop a theory of particle scattering in anisotropic media. That is, a medium in which the microstructure causes the mean free paths of the particles to become dependent on their direction of motion with respect to some fixed axis. The equation which results is similar to the normal, one-speed Boltzmann transport equation but has cross-sections which are functions of direction. This equation is solved for arbitrary cross-sectional dependence on direction in plane geometry.

scholarly journals Automatic reconstruction of polycrystalline ice microstructure from image analysis: application to the EPICA ice core at Dome Concordia, Antarctica

1999 ◽  
Vol 45 (151) ◽  
pp. 547-554 ◽  
Author(s):  
Michel Gay ◽  
Jerome Weiss
Keyword(s):  
Preliminary Analysis ◽  
Structural Parameters ◽  
Ice Core ◽  
Grain Morphology ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Thin Sections ◽  
Polycrystalline Ice ◽  
Analysis Application ◽  
The Mean

AbstractA digital image-processing approach is proposed which allows the extraction of two-dimensional polycrystalline ice microstructure (grain boundaries) from thin sections observed between cross-polarisers. It is based on image segmentation of colour images. The method is applied to the preliminary analysis of the shallow ( Holocene) ice of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. Structural parameters, such as the mean cross-sectional area, shape anisotropy and grain morphology, are obtained. The interest and limitations of this automatic procedure are discussed.

Cross-Sectional Reconstructions of Sickle Cell Hemoglobin Macrofibers.

1985 ◽  
Vol 43 ◽  
pp. 310-311
Author(s):  
Bridget Carragher ◽  
David A. Bluemke ◽  
Cathy E. Frantz ◽  
Michael J. Potel
Keyword(s):  
Sickle Cell ◽  
Cross Sections ◽  
Finite Thickness ◽  
Axial Direction ◽  
Structural Features ◽  
Real Space ◽  
Projection Algorithm ◽  
Helical Structures ◽  
Cross Sectional ◽  
Thin Sections

We have succeeded in performing two-dimensional cross sectional image reconstructions of sickle cell hemoglobin (HbS) macrofibers. Macrofibers are long helical structures which are intermediates in the crystallization of deoxygenated sickle cell hemoglobin at low pH. Earlier work has established that macrofibers are aggregates of Wishner-Love double strands which consist of 2 half-staggered HbS molecules repeating every 64 A in the axial direction. Thin sections of embedded aggregating macrofiber cross sections reveal a dumbbell like pattern of double strands (Figure 2a,b) that is similar to the a-axis projection of the crystal structure. Approximately 5 rows with 10 double strands per row were identified in the cross section, but structural features in the thin sections were obscured by an approximately 15 degree rotational blur due to the finite thickness (400 A) of the helical section, the ill defined boundaries of the section due to uneven staining, and apparent particle damage. These structural features have now been resolved in reconstructed cross sections obtained using a real space filtered back projection algorithm.

Aerodynamic behavior of wind turbines with polygonal cross- sectional tower

2021 ◽  
Author(s):  
Yong Chul Kim ◽  
Yukio Tamura
Keyword(s):  
Cross Section ◽  
Wind Turbines ◽  
Cross Sections ◽  
Lift Force ◽  
Circular Cross Section ◽  
Force Coefficient ◽  
Cross Sectional ◽  
The World ◽  
The Mean ◽  
Power Generation Systems

<p>Wind turbines are commonly used power generation systems around the world and their application is becoming increasingly widespread. Traditionally, circular‐cross‐section wind towers have been used, but recent upsizing of wind turbines has exposed weaknesses of these structures, including problems related to manufacturing and inadequate strength. Thus, the concept of site‐ assembled modular towers with polygonal cross‐sections such as octagonal and/or tetradecagonal has been proposed, but their wind‐resistant performances have not been clearly investigated. In the present study, the wind‐resistant performances of polygonal cross‐sectional towers were investigated through wind tunnel tests. It was thus found that the maximum force coefficient of the upper structure is larger than that of the tower, which makes the effect of cross‐sectional tower shape rather small. The mean and fluctuating lift force coefficients of a helical square cross‐sectional tower were quite small for cases of tower only and wind turbine.</p>

Sign in / Sign up

Export Citation Format

Share Document